Hydrogen is an important resource in the refining of crude oils and other hydrocarbon fractions. Refinery processes such as hydrotreatment, hydrocracking, and catalytic dewaxing, are dependent on the availability of hydrogen at a sufficiently high pressure as well as a sufficiently high purity.
Unfortunately, refineries tend to be net consumers of hydrogen. While processes such as reforming can result in generation of additional hydrogen, a typical refinery has greater demand for hydrogen than is available from processes in the refinery that generate hydrogen. External sources of hydrogen can be brought in to a refinery to make up the shortfall. However, such external hydrogen is usually expensive, so any savings in the amount of external hydrogen consumed is beneficial.
One potential way to reduce the amount of external hydrogen that is needed is to improve the use and recovery of hydrogen within a refinery. Refinery processes are typically performed using an excess of hydrogen, so that some hydrogen remains as an effluent or other product that exits a reactor. However, this hydrogen will typically have a higher level of impurities. Purifying and/or pressurizing this recycled hydrogen for use in the refinery can result in significant costs.
U.S. Pat. No. 4,398,926 describes a method for separating hydrogen from impurities using both a pressure swing adsorber unit and a membrane separator. The initial hydrogen-containing feed is passed through the membrane to produce a hydrogen enriched permeate and a retentate. The hydrogen enriched permeate is used as the feed gas to the pressure swing adsorber for producing a hydrogen product stream. When the pressure swing adsorber unit has reached the end of an adsorption step, the retentate from the membrane is co-fed through the adsorber unit to help sweep out the hydrogen product still in the unit.
U.S. Patent Application Publication No. 2009/0120839 describes systems and methods for hydrogen management for hydroprocessing units. The hydrogen management techniques include use of rapid cycle pressure swing adsorber units for recovery of hydrogen from the gaseous effluents of hydroprocessing units.
U.S. Pat. No. 7,591,879 describes systems and methods for employing rapid cycle pressure swing adsorber units in a refinery setting, such as in conjunction with hydroprocessing equipment.